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From: (no name) (no email)
Date: Sat Feb 03 2001 - 21:23:58 EST
In a message dated 02/03/2001 3:23:26 PM Eastern Standard Time,
writes:
> How expensive are the membranes for RO watermakers?
> What is their composition?
The membranes for my 25 GPH watermaker cost $500 per set of three. They are
some sort of plastic wound around a core tube.
The pressure vessel housings for the membranes are about $200 each.
> Can they be made? I can foresee problems with the enclosure
> at 1000psi...
Certainly one could make the pressure vessels, but not the membranes
themselves. The normal operating pressure is 800 psi as recommended in my
manual for longest life, but it can be raised as the membranes age to keep
output up, to about 950 psi.
> Why couldn't one of those $100 pressure washers be hooked
> up to drive the salt water through? Obviously running off
> a genset or something.
Any pump that can deliver about 2.5 GPM at 800 psi will work for my size
watermaker. Most are bronze, but mine is titanium and has a lifetime
warranty.
> Are all the electronic circuits really necessary?
No. They are a complicated convenience.
The electronics on my watermaker provide:
Automatic dump of product water if salinity is above a certain set point,
factory recommended at 550 ppm. This happens during start-up of the unit or
if a membrane should fail. When the salinity pcb failed, I simply waited for
one minute before I routed the product into the tank. Membrane failures of
this sort are rare, I'm told. Membranes normally fail by producing less and
less fresh water as time goes on.
Unit operating hour meter, useful for knowing when to change the HP pump oil.
Seawater temperature, for knowing if the membranes are producing good output
volume. As seawater temperature falls, output falls. There is a chart for
finding what the output would be for the standard of 78 degrees F.
Turning the LP and HP pumps on and off.
There is also a LCD screen that is supposed to tell you when certain
maintainence chores are to be done, but it is pure garbage.
Except for the hour meter, I would like to be rid of the electronics.
Another duty of the electronics is to protect the HP pump by turning if off
if it's feed water pressure should fall low enough (due to plugging of the 5
or 20 micron pre-filters) to make the HP pump cavitate. This can be done
simply using a Murphy gauge and a HP contactor with a trip line.
Use a 3-way valve to re-circulate the sea water so when you chemically clean
the membranes circulating the cleaner around and around the seawater circuit.
A product flow meter is nice to see how much fresh water you are making, but
not really necessary.
A high pressure gauge for adjusting the regulator.
A series of pressure gauges on the pre-filters to see when they need to be
serviced.
My recommendation is to get a Spectra watermaker. You can buy the unit
complete or buy the bits and pieces and build it as you like it. One gallon
per amp/hour can't be beat and you can run it with a solar panel or two. I
wish I had done that instead of buying the 240 vac unit I have now.
Norm
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